Large response - how to handle asynchronously

[Łukasz Osipiuk]

Hi Don,

On Sun, Mar 28, 2010 at 16:06, Don Park <donpark at docuverse.com> wrote:
> Łukasz,
>
> It seems to me that you are trying to do too much within messageReceived.
>
> I would just queue the request somewhere then handle it in another thread.

Separate queue and thread pool was a last resort for us but I hoped
there are some netty services that would do the job for me.
We will try to use ChunkedWriteHandler instead.

PS. I did not look into implementation of ChunkedWriteHandler - maybe
thread and queue is what it does :)

Regards, Łukasz Osipiuk


> You can implement blocking behavior around that queue too.
>
> Best,
>
> - Don
>
> On Mar 28, 2010, at 1:27 AM, Łukasz Osipiuk wrote:
>
>> Hi!
>>
>> We really need this solved.
>> If anybody had similar problem and have some thoughts on it we would
>> really appreciate help.
>>
>> Best regards, Łukasz Osipiuk
>>
>> On Thu, Mar 25, 2010 at 16:14, Łukasz Osipiuk <lukasz at osipiuk.net> wrote:
>>> Hi guys,
>>>
>>> We are implementing server application using Netty protocol framework
>>> and we have problem implementing handling of large responses.
>>> We will be handling many simultaneously connected clients.
>>> In protocol we are implementing, responses to client requests can be
>>> huge (lets assume that larger than server memory).
>>> While handling request we have to read part of response data from
>>> external storage - send it to client - wait until he receives the data
>>> and continue with next part.
>>>
>>> We approached problem with following code in handler (simplified
>>> version, no error handling and so on):
>>>
>>>   @Override
>>>   public void messageReceived(ChannelHandlerContext ctx, MessageEvent
>>> e) throws Exception {
>>>       XXXRequest req = (XXXRequest) e.getMessage();
>>>       writePartResponse(ctx, req);
>>>   }
>>>
>>>    private void writePartResponse(final ChannelHandlerContext ctx,
>>> final XXXRequest req) {
>>>        if (moreDataToBeRead(req)) {// anything more to be done?
>>>            XXXPartResponse resPart = readSomeData(req); // read some
>>> data from storage
>>>            ChannelFuture f = ctx.getChannel().write(resPart);
>>>            f.addListener(new ChannelFutureListener() {
>>>                public void operationComplete(ChannelFuture f_) throws
>>> Exception {
>>>                    writePartResponse(ctx, req);
>>>                }
>>>            });
>>>        }
>>>    }
>>>
>>> Above approach does not work.
>>>
>>> Problem 1.
>>>
>>> While handling request we have to block other client's requests  so
>>> they are not handled simultaneously.
>>> In above code when messageReceived() method terminates any pending
>>> client requests are delivered to handler and handled even though
>>> asynchronous handling of previous request might still be in progress.
>>> We do not know how to block handling of any pending requests.
>>>
>>> Problem 2.
>>>
>>> I client is quick enough to read data from socket f.addListener
>>> immediatelly triggers calling of futer.operationComplete in the same
>>> thread.
>>> This leads to StackOverflowError.
>>> (btw. It appears that StackOverflowError it is not handled correctly
>>> by netty in this place and application is not notified about it being
>>> thrown - handling of request is just silently terminated).
>>>
>>> Any way to avoid above problems?
>>> I guess the approach is broken - can anybody lead us how to implement
>>> such (trivial one might think) behaviour?
>>>
>>> Best regards, Łukasz Osipiuk
>>>
>>>
>>> --
>>> --
>>> Łukasz Osipiuk
>>> mailto:lukasz at osipiuk.net
>>>
>>
>>
>>
>> --
>> --
>> Łukasz Osipiuk
>> mailto:lukasz at osipiuk.net
>>
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>> netty-users at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/netty-users
>
>
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-- 
-- 
Łukasz Osipiuk
mailto:lukasz at osipiuk.net